Does Intense Aerobic Activity Grow Bigger Brains?

But intense aerobic activity can stimulate brain growth, develop a strong cardiovascular system, strengthen bones and produce that sought-after sense of wellbeing known as “runner’s high.” That’s how we evolved over millions of years.

Intense aerobic exercise sends more blood to the brain and helps produce drugs known as endocannabinoids – the same chemicals that found in marijuana.

UA anthropologist David A. Raichlen – himself a runner – wondered if other distance-running animals also produce those drugs.

“Maybe runner’s high is not some peculiar thing with humans. Maybe it’s an evolutionary payoff for doing something hard and painful that also helps them survive better, be healthier, hunt better or have more offspring,” he told National Public Radio’s Morning Edition.

Raichlen wondered if natural selection might have used neurobiological mechanisms to encourage exercise activity. As we evolved, did mankind continue to run because we’d become hard-wired to like it?

Humans, Dogs and Ferrets

That led to Raichlen’s research comparing distance-running dogs and humans with ferrets, a sedentary species. The results were published in the Journal of Experimental Biology by Raichlen, UA doctoral candidate Adam D. Foster and three colleagues.

Both humans and dogs run briskly on a treadmill for 30 minutes, then the researchers drew blood and compared the results to the slow-to-run ferrets. They also measured the dogs and humans as they walked, while the ferrets rested.

Raichlen told Science Daily that blood samples for both humans and dogs showed a significant increase in levels of endocannabinoids. They “rocked in the blood after a brisk run” and the humans reported being much happier after the exercise.

This was the first indication that dogs, and possibly other distance-running mammals, experience the naturally induced “runner’s high.”

Neither the humans nor the dogs showed any spike after walking. The ferrets had no increase throughout the study. This preliminary research suggests that a “reward response” to intense aerobic activity appears to be part of our evolutionary history.

Opportunity Leads to $10,000 Scholarship

Working with Dr. Raichlen on this project was a pivotal opportunity for Foster. “It really got me thinking broadly about using alternative animal models for testing questions related to human evolution. This project was certainly important for inspiring my dissertation research examining the role of skeletal plasticity in the evolution of bipedalism, using a rat model,” he said. “You could say this project was indirectly responsible for sparking the idea that led to the Force and Motion Foundation scholarship (an award of $10,000) and a National Science Foundation grant.”

At the UA Raichlen Lab he leads research on two pivotal aspects of human evolution – the shift to bipedal walking and the increase in aerobic activity as our predecessors began hunting and gathering. He works with graduate students to study evolutionary biomechanics and other factors that influenced human anatomy, physiology and neurobiology.

The Big Evolutionary Step

The way we walk – erect, with a long straight leg – is a fundamental characteristic of what makes us human. Longer legs mean a faster, more efficient stride. This was a species-changing evolution that ultimately led to the ability to run long distances. (Another key human evolution was the dexterity of opposable thumbs.)

When comparing the features of modern humans with the extinct human ancestor homo erectus, modern great apes and extinct Australopithecus, Raichlen found the more aerobically fit the primate, the greater its brain size is relation to its body.

This suggests that exercise alone can boost the body’s production of neurotrophins and brain-related growth factors – substances crucial for building and maintaining brain cells.

This intriguing news about the power of exercise comes at a time when modern technology makes it so easy for humans not to move – to be more like resting ferrets than race dogs.

Are we devolving? Eating more and moving less? Will our brains shrink? Should couch potatoes and computer geeks start running and seeking that brain-stimulating high?

Maybe – but don’t expect miracles.

Distance runner Raichlen has said, “inactive people may not be fit enough to hit the exercise intensity that leads to this sort of rewarding sensation.”

Yet they could build up their exercise tolerance to the point that they do cross the threshold and reach the level of intensity that produces the reward of “runner’s high.”